Well stimulation and intervention are typical activities to enhance the productivity of gas-bearing sandstone reservoirs and meet the increasing demand for energy. Many wells target sandstone formations that require stimulation to produce gas at an economical rate. Proppant fracturing is the preferred stimulation method for such reservoirs because it creates highly conductive pathways between the wellbore and the reservoir. Prior to any fracturing treatment, sufficient injectivity at an acceptable bottomhole treating pressure (BHTP) needs to be established. Depending on the reservoir quality, the task of breaking down the formation and establishing a sufficient injection rate may sometimes be challenging due to the high in-situ stress and compressive strength of the reservoir rock. Formation breakdown pressure can exceed the completion limitation due to stress alteration zones around the wellbore. For such cases, interventions using coiled tubing (CT) are often required to proceed with the hydraulic fracturing operation.
Two well-known remedial CT treatments are typically used to address wells with high breakdown pressures or low injection rates. The first is treatment by chemical means. Chemicals containing organic solvents or acids are squeezed into perforated intervals in the wellbore; subsequent soaking of the well with such chemicals can help remove some of the near-wellbore damage induced by drilling. The second is treatment using a mechanical approach; abrasive fluids containing gelled fluids and sand are jetted at high pressures through a nozzle at the target depth to create a cavern that connects the wellbore with virgin, non-stress-altered sections of the reservoir. More than 10 interventions performed over the past five years are analyzed in this paper. These include both abrasive jetting and chemical squeeze job techniques. Analysis indicates that only half of the abrasive jetting jobs were successful, and none of the chemical squeeze treatments provided positive results. Based on detailed analysis, ways forward were determined that will improve the success ratio for remedial actions using CT, including employing fiber-optic real-time telemetry to precisely place the bottomhole assembly and perforating with CT to optimize operational efficiency.
This paper provides an analysis of the well intervention practices that aid fracturing operations and prevent challenging situations such as high breakdown pressure that result in unsuccessful fracturing treatments. The knowledge obtained from this analysis can be extended to other regions where similar breakdown challenges exist.